Fig. 3027.
“First Method.—The most common method is technically termed by the forgeman, ‘finishing the piece before him.’ He begins with a staff or stave, as shown in [Fig. 3025], suspended by a chain from the crane, and made round for the convenience of manipulating under the steam hammer; this stave is used over and over again for many forgings, as it is merely the “porter” to carry the piece and enable it to be worked. The forging is begun by two or three slabs being placed on the stave as at s s s, and then inserted in the furnace. These slabs are flat blocks made up of pieces of scrap iron, which have been piled and heated, and then welded together. After being brought to a welding heat in the furnace, the slabs are withdrawn, placed under the steam hammer, and beaten down solid. The piece is then turned upside down, and two or three similar slabs placed on the opposite side, as shown at s s. When sufficient iron has been thus added to form the collar of the shaft (assuming it is to have a collar), it is rounded under the hammer, as at c, [Fig. 3026], and the body of the shaft next to the collar is roughly formed, as at d. More slabs, s s s, are added to bring out the body, and afterwards the crank itself is proceeded with, on the same plan. The piece will begin to assume the appearance of a, [Fig. 3026]. Then more slabs are welded on the top, as at s s s, till the depth of the crank is obtained, after which the forgeman proceeds to finish the collar and body of the shaft, as shown. The collar on being finished is cut all round, as shown at c d, [Fig. 3027], so that it may be more easily detached from the stave when the shaft is completed, leaving only sufficient connection to carry it till then. The forgeman then cuts the gable of the crank as at e g, and rounds up the body and neck as at b n, [Fig. 3027].
“This, it will be observed, is a speedy process, and would invariably be adopted if it were not attended with a very serious drawback; it is very hazardous to the solidity of the forging. For it will be easily understood that not above a third of the crank itself can be thus formed, because the iron at the neck n would not carry a greater mass; if the whole mass of the crank, or even the half of it, was formed before the body and neck of the shaft were finished, a proper heat could not be taken on the body and neck for finishing, without the neck giving way or rupturing. Indeed, as it is, the undue proportion often causes the shaft to be strained at this part, where most strength should be, so that it is rendered weak, and a flaw is developed which by-and-by causes it to be removed from the steamer as dangerous and useless, if indeed it does not break outright; so that the forgeman, if he adopts this method, must be very careful to proportion the amount of iron he has massed in the furnace to the size of the body he is finishing, otherwise the weakening above mentioned will take place. All marine engineers will easily recognise this defect, which frequently occurs, but the cause of which is probably not well understood. Such a flaw will present a similar appearance to that shown at f, [Fig. 3033], taken from an actual example.
Fig. 3028.
